Tepco has fixed the problem and is cleaning the water, but is still investigating what caused the leak

The
earthquake that rocked Japan this past March was an event that would have
lasting effects, and Japan's nuclear watchdog is still working to clean up the
mess almost four months later. Just this morning, tons of radioactive water was found
absorbing into the ground from Fukushima Daiichi's nuclear power plant.

Now, the Nuclear and Industrial Safety Agency has reported that 15 metric tons
of radioactive water has leaked from a storage tank at Fukushima Daiichi on the
Pacific Coast. The level of radiation in the water is low.

Large amounts of water have accumulated in the storage tanks because it was
used to cool the damaged reactors after the cooling systems were destroyed. The
leak was discovered Monday, and the system was shut down an hour and a half
after it started.

Tokyo Electric Power Co. (Tepco) has fixed the problem and restarted the system, but is
still investigating the cause of the leak. Tepco is also using a
decontamination system to clean the water so it can be recycled and continue
cooling the reactors.